Jump to content
Sign in to follow this  
jrgpots

Native Clay Glaze

Recommended Posts

About 2 months ago I made a terra sig from local clay.  It's a magnesium and iron rich bentonite. In its raw state it is purple and chocolate brown in oxidation. I don't know what it looks like in reduction yet.  It melt at cone 4-5.  I did triaxial blending of Gerstley borate, Nepheline syenite, and the clay with the results below.  The glaze has a satin finish with two coats and semi gloss finish with one coat.  It has a pleasing texture.  I like the tile that has the hole in the test tube.  Lemon juice test showed no discolorations.  There is no crazing.

 

Recipe: Gerstley bborate                6.52

            Neph syenite                     15.22

            local clay/bentonite           78.26

 

It was applied on bone dry clay and single -fired to reduce problems with the high bentonite and its COE.  I think I have my first stable home grown base glaze.

 

What colorants do you think I should try next?  

 

I have thought about adding RIO 6 - 8% to see if it will make a nice satin tenmuko that I could use as the base glase  for a cone 6 oil spot or hares hair glaze.  That is my aspiration.

 

Imput, critique, gut reactions are greatly appreciated.

 

Jedpost-26461-0-73266800-1393987052_thumb.jpg

post-26461-0-73266800-1393987052_thumb.jpg

Babs likes this

Share this post


Link to post
Share on other sites

we fire to ^8-9 but maybe I can offer a couple starting points

 

80 local clay

15 local calcium (whiting)

5 rio

2 light mgco3

 

it had an annoying tendency to blister - nothing serious just the odd 3 or 4 blisters every load. it was tolerable but annoying.

 

I spent some time trying to puzzle them away but gave up after finally figuring out a decent jasper.

 

there is another black recipe I can share with certainty but unfortunately I'm away from my little black book atm and can't remember the jasper exactly.

Share this post


Link to post
Share on other sites

the jasper has 10 grams bone ash, black iron oxide, whiting and I pretty sure 10 grams gb as well. the other couple ingredients im unsure of and it adds up to 114 or something

 

your 'clay' test results sound very familiar

 

the purplish oil spotting I remember with 10+% of rio was encouraging but I got sidetracked after findings spots of red. iirc 12% rio was the most I tried.

Share this post


Link to post
Share on other sites

You might consider 2 glazes, the one you have as the base with more iron 5%, the other the base plus 3134 frit in increments of 10% with about 4-5% rutile for a breaking gloss over the base

Wyndham

Share this post


Link to post
Share on other sites

You might consider 2 glazes, the one you have as the base with more iron 5%, the other the base plus 3134 frit in increments of 10% with about 4-5% rutile for a breaking gloss over the base

Wyndham

That sounds interesting. I'll be making more test tiles.

 

Jed

Share this post


Link to post
Share on other sites

This is my native clay - a red terra cotta.  Recipe - terra cotta 80; Frit 3134 20.

You can see the little tea dust crystals.

 

post-11430-0-92075900-1394154381_thumb.jpg

post-11430-0-92075900-1394154381_thumb.jpg

Share this post


Link to post
Share on other sites

This is my native clay - a red terra cotta.  Recipe - terra cotta 80; Frit 3134 20.

You can see the little tea dust crystals.

Wow! That's beautiful. Crazing quite a bit though. You could try a line blend of flint-5%.10%15%. To see if you can get a better fit. Of course the frit is also a glass former.

TJR.

Share this post


Link to post
Share on other sites

here is that jasper

 

local clay 50

volcanic ash 10

bone ash 10

silica 10

gerstley borate 10

black iron oxide 10

spodumene 10

kona f4 4

mgco3 3

 

all in grams

 

nice red breaking black with touches of purple at ^8.5-9 in oxidation

Share this post


Link to post
Share on other sites

O.K.

I had to rewrite your formula so that it looks more like a percentage

local clay  50

volc. ash  10

Flint/silica 10

Ger. Bor.   10

Spodumene10

Total ---------100

Kona f4      4

Mang. carb 3

Black Iron   10

 

So looking at the percentage now, you still have Kona F4 which is a Soda flux. I left it out of the 100% total just for ease of reading the recipe.

If you look at your manganese-you have 3% in the glaze.

You also have a huge amount of black iron.

I would try a line blend without either the manganese or the iron to see what your base looks like.

Then you can add 1% iron, then 2, then 4% etc.

If you were firing in reduction, your glaze would be really dark, and probably run.

Remember, test,test,test, and show us the results.

TJR.

Share this post


Link to post
Share on other sites

thanks TJR

 

im online very infrequently and wanted to respond here a few times but this phone tech is ... alien

 

this is one of my success stories - it only took a few years but after giving up for a year or so I had a thought and threw a hail mary of sorts

 

the recipe should read magnesium carbonate rather than manganese and is definitely approaching what I would call iron saturated?

 

it is well behaved at ^9 and, when happy, shows no off browns and much maroon/purple character

 

if I was to submit a glaze to cm this would be the first one of ? 3

Share this post


Link to post
Share on other sites

Do you have a pic for your latest tweek in the recipe?  I'd love to see it.

 

Jed

I get to live near potter types for the next bit so I thought I'd dig this old thread up with a picture.

 

Hopefully I can sneak a test or three into a few different kilns/atmospheres. I miss testing glaze ideas.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×

Important Information

By using this site, you agree to our Terms of Use.